1. Field of the Invention
The present invention relates to an electronic device such as a notebook personal computer equipped with a cooling unit including a radiator and a fan and, more particularly, to an electronic device which detects performance degradation of a cooling unit.
2. Description of the Related Art
An electronic device such as a notebook personal computer commonly uses a cooling unit including a heat disperser, heat pipe, radiator, and fan to cool a heat generating portion such as a CPU. Heat from the heat generating portion is transferred to the heat disperser that is in contact with it and transported to the radiator through the heat pipe. The fan takes in air from an opening formed in the case of the electronic device and sends the air to the radiator. The air cools the radiator and the heat generating portion, too.
The airflow generated by driving the fan contains dust in the air, which comes into the radiator. The dust is partially discharged outside through the radiator, but some adheres particularly to its inlet, builds up gradually in the course of time, and impedes the airflow, finally affecting the cooling performance.
Several solutions are available, including detecting clogging in a dust-trap member such as a filter mounted on the radiator, cooling unit, or case opening, and at certain level of clogging, prompting the user to exchange the dust-trap member or operate a dust-removal unit incorporated in the electronic device, or causing an internal unit of the electronic device or another electronic device connected via a network to issue an instruction to automatically remove dust.
One of systems to implement this procedure detects dust clogging based on an increase in the rotational speed of the fan. For example, JP-A 2004-63993 (KOKAI) describes a technique of presetting a predetermined rotational speed in a memory, and advising filter exchange upon detecting dust clogging by comparing a detected rotational speed with the predetermined rotational speed. For example, JP-A 2007-189183 (KOKAI) describes a technique of detecting disparity between an actual rotational speed and a controlled rotational speed and recommending cleaning of a dust collector for scraping out dust.
If the fan that sends air to cool the radiator is operated alone, for example, the rotational speed at a predetermined applied duty ratio gradually decreases. The causes include degradation of lubricant used for the bearing of the fan and dust adhering near the fan rotation unit. This phenomenon cancels the increase in the rotational speed of the fan caused by increasing clogging. It therefore becomes difficult to detect dust clogging.